The present invention relates to a modular cold generating apparatus.
The prior art disclosed cold generating apparatus operating in an autonomous manner, i.e. without any external energy supply and having no moving part. Thus, they are characterized by a high degree of simplicity and excellent reliability. Such apparatus are based on the known property of the earth's atmosphere of permitting the passage in a preferred manner of radiation between 8 and 13.mu. and between 16 and 25.mu.. Part of the radiation emitted by black bodies falls within the above ranges.
It is known that a black body is a body which completely absorbs the radiation which it receives, no matter what its wavelength. Such a body is in thermodynamic equilibrium with the radiation which it receives and with the radiation which it emits. In principle, the emissivity of a black body is equal to unity and extends throughout the spectrum, particularly in the atmospheric windows. When a black body is placed in the atmosphere, the energy portion which it radiates in such windows is transmitted into space, almost without accumulation. This leads to a cooling of the emitting body. The temperature drop undergone by the body is limited if parasitic heat exchanges take place with the ambient air or with the ground either by convection, or via condensation phenomena linked with the degree of humidity of the air.
In known cold generating apparatus, the body undergoing cooling due to its radiation through atmospheric windows is thermally linked with a material have a solid--liquid transition in the vicinity of the operating temperature of the apparatus. This thermal link takes place by means of a heat pipe, which acts as a thermal diode, ensuring the thermal connection only in the direction from the material to the black body. This leads to a reduction in the temperature of the material causing its solidification, without any reverse transformation of the solid phase to the liquid phase taking place, because the transfer of heat which could take place from the radiating body is blocked by the thermal diode. Thus, the apparatus produces cold and stores it.
FIG. 1 shows such a known cold generation apparatus. This apparatus comprises a radiating surface 2 connected thermally with a heat pipe 4 constituting a thermal diode. The lower part 6 of the heat duct is provided with ribs 8, which serve to increase the exchange surface betwen the fusible material and the heat pipe. It is immersed within a fusible material which is liquid at the daytime ambient temperature, e.g. water, said reservoir being thermally insulated from the ground and is tightly sealed by means of its walls, which are e.g. made from a plastics material. This storage reservoir is not shown in FIG. 1.
In its upper part, the heat pipe 4 has a discontinuous capillary structure enabling it to perform the function of a thermal diode. When the radiating surface is at a temperature above that of the storage reservoir, the condensed liquid of the heat duct remains in the bottom part thereof and it is impossible for heat to be transferred by the heat pipe.
The heat pipe is filled with a compound, whose evaporation point is compatible with the operating temperature of the apparatus, e.g. freon or ammonia.
However, the aforementioned cold generating apparatus has a certain number of disadvantages. The construction of the heat pipe or pipes ensuring the thermal connection between the cold storage means and the radiating surface is of a complex nature, leading to high manufacturing costs. The fins operate under thermal conduction conditions, so that they do not have a very good efficiency. Thus, the thermal connection between the storage material and the heat duct 4 is relatively poor.
In addition, the radiating surface 2 also functions under thermal conduction conditions. Therefore, the thermal connection between the radiation surface and the heat duct is also relatively poor.
Finally, such apparatus have significant overall dimensions, similar to that of an open umbrella. Therefore, they are not very suitable for transportation. When it is necessary to transport a large number of such apparatus over long distances, the transportation costs are very high.